The present invention relates generally to halftone screening processes and, more particularly, to a method and system for metadata controlled multi-configured halftone screening.
Halftone screening processes are processes used to transform a continuous-tone image into a binary image that may be rendered and perceived by an observer as the original continuous-tone image. Halftone screening processes typically apply one or more halftone screens to a continuous-tone image. The result is binary image that appears to be made up of individual dots when viewed up close; but, when observed from a typical viewing distance, appears as the original continuous-tone image. Currently, halftone screening processes are used in printing devices such as laser printers, dot matrix printers, and inkjet printers; and the like.
Halftoning is necessary because printing devices are not capable of producing all of the shades or colors contained in continuous tone images. For example, a laser printer may have only one color of ink; typically, black. There are no grays. Halftoning permits the appearance of a number of shades of gray.
Color laser printers are similar, though more complex. Again, color laser printers are not capable of reproducing all of the colors that may be found in a continuous-tone image. Commonly, color printers contain only four colors of ink; namely, cyan, magenta, yellow, and black. For color reproduction, four different screens are required along with three different filters. The filters break the continuous-tone image down into the four colors of ink, allowing simulation of all the colors found in the continuous-tone image.
Halftone screens are created using screen frequencies measured in lines per inch (lpi), and as such, a screen frequency is often represented by a grid. Each square in the grid then represents a halftone cell capable of holding a halftone dot. Higher screen frequencies produce finer halftone screens, while lower screen frequencies produce coarser halftone screens. Further, multiple screen frequencies are represented by multiple grids or halftone screens.
Screen frequencies are selected based on the contents of a continuous-tone image. For example, a continuous-tone image may contain a mixture of images, fonts, and office graphics. Further, a “smooth” halftone is suitably used for the images, while a “detail” halftone is suitably used for the fonts and office graphics. When two portions of a continuous-tone image require different halftones, first one halftone is selected for a first portion and then a second halftone is selected for the second portion. Such an approach works reasonably well on an area-by-areas basis. However, switching between halftones within a continuous-tone image containing a mixture of images, fonts and office graphics is difficult. Moreover, the processing when using multiple halftone screens can become slow and burdensome.
Thus, there exists a need for a method and system which eases transitions between halftones as applied to continuous-tone images.